The research proposed here will use the powerful tool of the transgenic mouse to examine the early events and mechanisms that regulate the production of autoantibodies capable of mediating renal damage. This work is based on recognition of the central role of the Ig receptor in determining B cell responses and participating in immunologic intercellular and idiotypic interactions, as well as contributing to the pathogenic potential of autoantibodies. The proposed studies evolved from our identification of glomerular immune-deposit forming autoantibodies that target the intrinsic renal antigen, laminin, and that express variable regions that appear to be targeted by abnormal immunoregulation. These Ig are encoded by conserved VH genes that define a major autoimmune idiotype and recur frequently among anti-dsDNA and anti-laminin Ig, and among Ig capable of transferring disease to naive animals. Furthermore, the recurrent use of unmutated VH genes suggests the presence of these potentially nephritogenic B cells within the normal preimmune repertoire. The studies proposed here will test the hypothesis that these specific disease-associated Ig receptors are targets of immunoregulation to prevent their activation in the normal immune milieu, and that perturbation of these pathways due to a genetic autoimmune predisposition and/or exogenous immunostimulation can lead to autoimmunity. For this purpose, the preimmune repertoire will be experimentally biased through the generation of transgenic mice. These will carry in their germlines functionally rearranged genes such that the majority of the B cells express predetermined anti-self specificities with pathogenic potential. With this tool, the interactions of these specific pathogenic determinants within the complex immunologic network of the whole organism can be examined. In vivo and in vitro assays of B cell proliferation, differentiation and antigen binding and monoclonal Ig technology will be employed to compare the developmental fate, state of immunologic competence, expression of autoreactivity and pathogenicity of the resulting B cells and Ig under different biologically relevant conditions. 1) within the context of the normal immunologic milieu of nonautoimmune C57BL/6 mice; 2) under the influence of the MRL/lpr autoimmune background; and 3) under the influence of exogenous antigenic (DNA and laminin) and nonspecific (LPS) immunostimulation. Initial studies will determine if and how autoimmunity is avoided in the normal host. This will provide a background for evaluation of manipulations designed to alter disease expression. Ultimately, we hope to generate a model of autoimmunity using Ig that target an intrinsic renal antigen. The results should contribute to our understanding of the immunologic dysregulation that leads to autoimmune renal disease and systemic autoimmunity, and ultimately contribute to the development of new interventions.